Anode and method of operating an electrolysis cell

ABSTRACT

The invention relates to an anode for electrowinning process in an electrolytic cell, and the method of operation thereof, having cell walls and a cell bottom for holding an electrolyte and electrolyte feeding means, which anode comprises a hanger bar for supporting the anode, a conducting rod for distributing the current, an anode body having at least partly conductive structure. The anode body allows electrolyte penetration and is at least partly covered by electrocatalytic coating, when in connection with the anode there is arranged a non-conductive element, which is restricted to the conductive structure of the anode body, at least from its one side, and which non-conductive element is arranged at a distance A from the electrolyte surface level, when the non-conductive element provides a means for attaching the anode to the cell.

FIELD OF THE INVENTION

The invention relates to a new kind of anode to be used in electrowinning. The invention also relates to a method of operating an electrolysis cell to be used in the electrowinning of metals.

Electrowinning is a process where a metal dissolved in an electrolyte is reduced on a cathode by means of an electrical current. In electrowinning a current is passed through the anode through the electrolyte solution containing the metal value so that the metal value is extracted as it is deposited in an electroplating process onto the cathode. When an electrical current is applied to the sulfate based electrolysis system, metal is precipitated on the surface of the cathode and water decomposes on the anode where acid and oxygen are formed. Electrowinning takes place in an electrolytic cell that contains a number of anodes and a number of cathodes arranged in an alternating manner. The commercial use of electrowinning requires a large number of cathodes and anodes in a single electrolytic cell. One type of anode used in electrowinning has been lead based anode, which could have a negative effect on the quality of copper deposited. One significant disadvantage of using such lead based anodes is that during electrowinning operations small amounts of lead are released from the surface of the anode, which causes the undesirable particulates to be suspended in the electrolyte. In addition, the lead sludge must be cleaned periodically from the cell bottom e.g. every 45 to 90 days, and during this time the electrowinning cell is not producing metal.

One issue in electrowinning processes is a rather high cell voltage leading to increased energy consumption. Due to high energy consumption in electrowinning and low corrosion resistance of previous anodes, there has been a need to investigate better anode materials in electrowinning. Mixed metal oxide (MMO) coated anodes consist of conductive mixed metal oxide coatings on valve metal substrates, usually titanium or nickel. Dimensionally Stable Anode or DSA® is a well-known type of MMO-coated anode. When the MMO-coated anodes are used in sulfate based electrowinning the cell can be operated at a lower cell voltage than when lead based anodes are used. One type of dimensionally stable anode is presented in patent publication US4134806, where the idea is to stabilize current distribution between the DSA anode and cathode by thickening the DSA anode structure in the border areas. Publication US 20100276281 presents the anode for use in electrowinning cells. According to the publication the electrode includes a hanger bar and an electrode body including at least one conductor rod and a substrate, a connection coupling the hanger bar and the at least one conductor rod, and a seal isolating the connection. An electrode comprises a hanger bar including at least one recessed hole, and an electrode body comprising at least one conductor rod press fit into said at least one recessed hole and a substrate coupled to said conductor rod.

Past research and development efforts have focused on ways to increase production capacity per plant area for copper electrowinning, which directly impacts on the cost-effectiveness of the electrowinning process. To increase the production of the electrolysis plant and cell, it is desirable to increase the current density during electrolysis, and achieve a higher deposition rate of copper on the cathodes. The current density on the cathode side is limited by the quality of the copper deposited, as due to the increased overvoltage on the cathodes more impurities are deposited with increasing current density. In addition, increasing the current density also leads to an increase in the corrosion rate of lead from lead anodes and consequently more lead circulates in the electrolyte and lead can be included in the cathodes, necessitating an increase in the frequency of cell cleaning to control lead and decreasing the production rate.

Due to high investment and operating costs of the electrolysis plants and cathode processing plants comprising of a crane and stripping machines, which are combined in the so-called tankhouse, attempts have been made for quite some time at increasing the economic efficiency of both the refining electrolysis and the extraction/electrowinning electrolysis. This largely depends on the efficiency of the electrolysis as well as on the number of the cathode movements and therefore on the amount of copper deposited per cathode. One way to decrease tankhouse capital expenses is by increasing the length of cathode, thus increasing the production capacity per cell without the need to increase the current density, the plant area or the number of electrolytic cells.

Publication WO 2005/080640 presents a process for electrochemically winning or refining copper, where the idea of the invention is to increase the copper loading per cathode. To increase the economic efficiency of such processes and plants, it is proposed in accordance with the publication to immerse at least one cathode into the electrolyte over a length of at least 1.2 meters during operation of the electrolysis.

Still problems can occur when using cathodes with great length. When using lead anodes with jumbo cathodes i.e. cathodes of great length, warping of the anode during electrowinning may occur and cause short circuits to the process. There can be problems especially with the first and last anodes in a cell, with current flowing only on one side of the anode, which may cause warping or creep deformation of the anode. Warping leads to an increased number of short circuits and a lower current efficiency. If lead anodes are used with jumbo cathodes, more frequent cell maintenance is needed to remove the lead sludge from the cell. In addition, for an even current distribution it is beneficial to position the anodes at equal distances from the cathodes. In order to avoid such issues or problems there has been a need to develop a new kind of anode to be used with long cathodes with a rigid structure and located in the right position in the cell.

OBJECTIVE OF THE INVENTION

An object of the invention is to provide an anode for electrowinning process, especially when the anode is to be used with “jumbo” cathodes having a great length (of 1.2 m or longer) and for avoiding problems stabilizing the position of the anode inside the electrolytic cell.

SHORT DESCRIPTION OF THE INVENTION

The anode and the method of the invention are characterized by the definitions of independent claims. Preferred embodiments of the invention are defined in the dependent claims.

The invention presents an anode for an electrowinning process in an electrolytic cell having cell walls and a bottom cell for holding an electrolyte and electrolyte feeding means. The anode comprises of a hanger bar for supporting the anode, a conducting rod for distributing the current to the anode, an anode body having at least partly conductive structure, which anode body allows the penetration of the electrolyte and is at least partly covered by electrocatalytic coating, when in connection with the anode there is arranged a non-conductive element, which is restricted to the conductive structure of the anode body at least from its one side and which non-conductive element is arranged at a distance A from the electrolyte surface level, when the non-conductive element provides a means for attaching the anode to the cell. By using of anode presented in this invention many problems in a process for electrowinning can be avoided. According to the embodiment of the invention the length A is arranged to be between 0.3-2 meters, which depends on the size of the electrodes and process parameters.

According to the one embodiment of the invention the non-conductive element of the anode is formed by excluding part of the anode body from electrocatalytic coating, for example at least 2 percent of the anode surface is excluded from electrocatalytic coating.

According to one embodiment of the invention the non-conductive element is made of at least one non-conductive object attached to the anode body.

According to another embodiment of the invention the anode is being attached into the electrolytic cell by anchoring elements located in the cell bottom, in the cell wall, in the electrolyte feeding means or attached to the cathode next to the anode.

According to the invention the conductive structure of the anode body consists of a mesh structure, including preferably at least one of the following; Ti, Ni, Pb, Ta, Zr or Nb and the electrocatalytic coating consists of a Pt-group metal oxide or a mixture of metal oxides.

According to another embodiment of the invention the height B between the upper part of the non-conductive element and anode bottom surface is arranged to be between 0.05-0.3 m.

The invention also describes a method of operating an electrolysis cell to be used in the electrowinning of metal, when metal is electrodeposited on the cathode surface from an electrolyte solution in an electrolytic cell having cell walls and a cell bottom, which cell contains electrolyte where anodes and cathodes are immersed in alternating fashion, in which the anode is supported by a hanger bar on the conducting rod, which distributes the current to the anode, when the anode body has at least a partly conductive structure allowing the penetration of the electrolyte and an electrocatalytic coating, when the anode is attached inside the electrolytic cell by a non-conductive element arranged in connection with the anode, which non-conductive element is restricted to the conductive structure of the anode body at least from its one side and which non-conductive element is arranged at a distance A from the electrolyte surface level. According to the embodiment of the invention the anode is attached into the electrolytic cell bottom by anchoring elements.

According to the different embodiments of the method the anode is attached into the electrolytic cell wall, into the electrolyte feeding means or the cathode next to the anode by anchoring elements.

According to one embodiment of the invention the electrolyte is fed at least from two manifolds in the cell, when the other one is at the bottom of the cell.

According to one embodiment of the invention the anode could be used in the electrowinning of the metal copper, Cu.

There are many advantages of using the anode according to the invention. The anode can easily be attached in the cell, anode warping is avoided, good mixing effect of electrolyte inside the cell is reached by using the anode according to the invention. Also copper growth on the cathode surface will be more even. When using a flow-through anode with electrolyte feeding vertically in the middle of the cell, good electrolyte mixing is obtained and metal ion concentration gradients can be avoided. Better anode attaching and anchoring in the cell can be achieved by coating only part of the surface of the anode with the electrocatalytic coating.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, illustrate embodiments of the invention and together with the description help to explain the principles of the invention. In the drawings:

FIG. 1 schematically shows an anode according to the invention, where the non-conductive part of the anode is part of the anode body.

FIG. 2 shows another embodiment of the anode, where the non-conductive element is attached to the anode.

FIG. 3 a schematically shows an anode according to the invention, where the anchoring elements are located on the electrolytic cell bottom.

FIG. 3 b schematically shows an anode according to the invention, where the anchoring elements are located on the electrolytic cell walls.

FIG. 3 c schematically shows an anode according to the invention, where the anchoring elements are located on the electrolyte feeding means.

FIG. 3 d schematically shows an anode according to the invention, where the non-conductive element is attached to the anode and attached to the anchoring elements.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

FIGS. 1 and 2 shows an anode 1 for electrowinning of metals, such as copper in an electrolytic cell 2 having cell walls 3 and cell bottom 4 for holding an electrolyte 5. The anode comprises of a hanger bar 7 for supporting the anode on the conducting rod 8, which distributes the current to the anode, an anode body 9 having at least partly conductive structure allowing the penetration of the electrolyte and an electrocatalytic coating. According to the invention there is arranged a non-conductive element 10, 12, 14 in connection with the anode 1 at a distance A from the electrolyte surface level 11, when the distance A is arranged to be at an interval 0.3-2 meter. This depends on the size of the anode used. The non-conductive element 10, 12, 14 provides means for attaching the anode 1 inside the electrolytic cell 4, which is important when using long anodes with long cathodes. When using long cathodes, it is important that the anode is fixed and rigid in its place and possible warping of the anode is prevented. The non-conductive element consists of any suitable material that is not electrically conductive and could be selected based on the process needs. It is possible that the non-conductive element could consist of several pieces or is made from one piece.

FIGS. 3 a, 3 b, 3 c and 3 d describe different ways for attaching the anode inside the electrolytic cell 4. The non-conductive element 10, 12, 14 of the anode provides means for attaching the anode 1 for example in the cell bottom 3, to the walls 2 or to the electrolyte feeding means 6 by anchoring elements 13, which are attached to the non-conductive elements. It is also possible to attach the anode next to the cathode inside the electrolytic cell (not shown in figures). When the anode is attached to the cathode by using non-conductive element, it means that it acts as a spacer, which is known to be used to align the electrodes and separate them at a fixed distance from each other in order the electrolytic process to function. One way for attaching the anode is presented in FIG. 3 b, when the anchoring elements 13 are located in both sides of the anode, which anchoring elements are attached to the non-conductive element 14 and from its other side to the electrolytic cell walls 2. By attaching the anchoring elements 13 to the electrolyte feeding means 6, as presented in FIG. 3 c, it saves space inside the electrolytic cell.

When using a long anode, it is important that the anode is rigid and straight and positioned from even distance from the adjacent cathodes. According to the invention the anode can be anchored inside electrolytic cell 4 by supportive anchoring elements 13, which could be of any shape (e.g. V-neck) and suitable for attaching them to the non-conductive elements 10, 12, 14. The electrolytic cell may be used for electrowinning of several metal values. An electrowinning cell as described herein may be configured for the extraction of a variety of metal values. FIG. 3 d schematically shows an anode, where the non-conductive element 12 is attached to the anode and attached to the anchoring elements 13. It is possible that the non-conductive element is attached to the cathode next to the anode, when the non-conductive element functions as a cathode guide, i.e. during cathode harvests it guides the cathode into the correct position and prevents any contact between the cathode and the anode body.

According to the invention the distance between electrolyte surface level 11 and the non-conductive element, meaning length A is arranged to be in interval 0.3-2 meter when the height B between the upper part 16 of the non-conductive element 10,12,14 and anode bottom surface 15 is arranged to be between 0.05-0.3 m. Then the immersion of the anode is enough to be used with long cathodes. One way is to form the non-conductive element 10, 12, 14 of the anode 1 is by excluding the anode body 9 from electrocatalytic coating when at least 2 percent of the anode 1 surface is excluded from electrocatalytic coating. When part of the surface is left without conductive electrocatalytic surface, electric current can be shielded and anode can be placed on the cell bottom without problematic edge deposit growth on the cathode bottom. The conductive structure of the anode body consists for example of a mesh structure allowing the penetration of the electrolyte, when the anode mesh consists of preferably one of the following metals; Ti, Ni, Pb, Ta, Zr or Nb. Catalytic coating preferably consists of Pt-group metal oxide.

It is apparent to a person skilled in the art that as technology advanced, the basic idea of the invention can be implemented in various ways. The invention and its embodiments are therefore not restricted to the above examples, but they may vary within the scope of the claims. 

1. An anode (1) for electrowinning process in an electrolytic cell (4) having cell walls (2) and cell bottom (3) for holding an electrolyte and electrolyte feeding means (6), which anode comprises of a hanger bar (7) for supporting the anode, a conducting rod (8), for distributing the current to the anode, an anode body (9) having at least a partly conductive structure, which anode body allows the penetration of the electrolyte and is at least partly covered by electrocatalytic coating, characterized in that in connection with the anode (1) there is arranged a non-conductive element (10, 12, 14), which is restricted to the conductive structure of the anode body (9) at least from its one side and which non-conductive element is arranged at a distance A from the electrolyte surface level (11), when the non-conductive element provides a means for attaching the anode to the electrolytic cell (4).
 2. Anode according to the claim 1, characterized in that the length A is arranged to be between 0.3-2 meters.
 3. Anode according to the claim 1 or 2, characterized in that the non-conductive element (10, 14) of the anode (1) is formed by excluding part of the anode body (9) from electrocatalytic coating.
 4. Anode according to claim 3, characterized in that at least 2 percent of the anode surface is excluded from electrocatalytic coating.
 5. Anode according to any of the claims 1-2, characterized in that the non-conductive element is made of at least one non-conductive object (12) attached to the anode body (9).
 6. Anode according to any of the claims 1-5, characterized in that the anode is being attached into the electrolytic cell (4) by anchoring elements (13) located in the cell bottom (3).
 7. Anode according to any of the claims 1-5, characterized in that the anode is being attached into the electrolytic cell by anchoring elements (13) located in the cell wall.
 8. Anode according to any of the claims 1-5, characterized in that the anode is being attached into the electrolytic cell by anchoring elements (13) located in the electrolyte feeding means (6).
 9. Anode according to any of the claims 1-5, characterized in that the anode is being attached into the electrolytic cell by anchoring elements (13) attached to the cathode next to the anode (1).
 10. Anode according to any of the claims 1-9, characterized in that the conductive structure of the anode body (9) consists of a mesh structure, including preferably at least one of the following; Ti, Ni, Pb, Ta, Zr or Nb.
 11. Anode according to claim 1, characterized in that the electrocatalytic coating is consists of a Pt-group metal oxide or a mixture of metal oxides.
 12. Anode according to any of the claims 1-11, characterized in that the height B between the upper part (16) of the non-conductive element (10,12,14) and anode bottom surface (15) is arranged to be between 0.05-0.3 m.
 13. A method of operating an electrolysis cell to be used in the electrowinning of metal, when metal is electrodeposited on the cathode surface from an electrolyte solution (5) in an electrolytic cell (4) having cell walls (2) and cell bottom (3), which cell (4) contains electrolyte (5) where anodes (1) and cathodes are immersed in alternating fashion, in which the anode is supported by a hanger bar (7) on the conducting rod, which distributes the current to the anode, when the anode body (9) has at least partly conductive structure allowing the penetration of the electrolyte and an electrocatalytic coating, characterized in that the anode is attached inside the electrolytic cell (4) by a non-conductive element (10, 12, 14) arranged in connection with the anode (1), which non-conductive element is restricted to the conductive structure of the anode body at least from its one side and which non-conductive element is arranged at a distance A from the electrolyte surface level (11).
 14. Method according to claim 13, characterized in that the anode is attached into the electrolytic cell bottom (3) by anchoring elements (13).
 15. Method according to claim 13, characterized in that the anode is attached into the electrolytic cell wall (2) by anchoring elements.
 16. Method according to claim 13, characterized in that the anode is attached into the electrolyte feeding means (6) by anchoring elements (13).
 17. Method according to claim 13, characterized in that the anode is attached into the cathode next to the anode by anchoring elements (13).
 18. Method according to any of the claims 13-17, characterized in that the electrolyte is fed at least from two manifolds in the cell, when the other one is at the is bottom of the cell.
 19. Use of the anode according to any one of the claims 1 to 12 in the electrowinning of the metal copper, Cu. 